Field of the Invention
The present invention relates to a tank gauge and more particularly a sealed tank gauge for use in measuring the level of liquids.
It is well known that a tank gauge in relation to an oil tank must be sealed in order to prevent gases such as hydrogen sulfide gases from escaping the tank. For this reason, many tank gauges have been developed which are properly sealed and explosion proof but which render the reading of such gauges difficult. Tank gauges such as described in U.S. Pat. No. 1,656,705 Gould, Jan. 17, 1928; U.S. Pat. No. 1,933,522, Edwards, Oct. 31, 1933; U.S. Pat. No. 2,216,035, Lang, Sept. 24, 1940 and U.S. Pat. No. 3,500,546, Pilcher, Mar. 17, 1970 provide methods of indirectly measuring the liquid level in a tank by telemetric systems, such as described in all of the patents with the exception of Lang. It is important as mentioned above, to keep the float and suspension cable system used for measuring the level of oil in a sealed, explosion-proof housing which communicates with the tank. However, in these systems, both the counterweight and the pulleys on which they are mounted are within the tank and/or the housing for the pulleys. In the Lang patent, a complicated system is provided wherein the counterweight is in the form of an indicator giving a direct reading of the level of oil in the tank. However, in Lang, the cable of the indicator on the outside of the housing must be kept in a completely sealed pipe and housing system as shown in FIG. 1 of the Lang Patent.